Project Summary According to the World Health Organization, obesity has reached epidemic proportions worldwide, with at least 2.8 million people dying each year as a result of being overweight or obese. Obesity is a major risk factor for metabolic diseases such as nonalcoholic fatty liver disease and type 2 diabetes. The development of long-term strategies for obesity prevention and therapy requires a comprehensive understanding of metabolic regulatory networks that control adiposity. At the center of these networks are proteins of the lipin family that have been identified as crucial determinants of adipose tissue development and fat storage. Lipins are regulated in response to nutrients by insulin and the nutrient-sensitive TOR signaling pathway. In particular the TOR pathway controls movement of lipins into the cell nucleus where they participate in gene regulation. The major objective of this research project is to determine how lipins that are expressed in non-adipose tissues, in particular the endocrine system, contribute to metabolic regulation. The project will use a predominantly genetic approach to identify novel roles of lipins using the model organism Drosophila melanogaster. Besides the elaborate genetic tools that allow studies in whole, physiologically intact animals, Drosophila has the advantage of having only one Lipin gene, in contrast to three genes that complicate studies in humans and mammalian model systems. Using the novel CRISPR/Cas9 technology, we will create a series of Drosophila mutants carrying altered Lipin genes, including a mutant that expresses Lipin lacking the ability to enter the cell nucleus and, thus, participate in gene regulation, and a mutant expressing Lipin protein that exhibits constitutive nuclear localization. Other mutants will express Lipin proteins that cannot be modified by post- translational modifications of specific amino acid residues, which may affect nuclear translocation and other functions of the protein. These mutants, in combination with Lipin transgene expression in specific tissues, are expected to shed light on functions of lipins in non-adipose tissues and on novel signaling pathways that may participate in the functional regulation of lipins. Finally, the project will examine the role of Lipin in the production of a major steroid hormone that controls metabolism and development of Drosophila. It is anticipated that results of this aim will set the stage for the discovery of roles of lipins in endocrine tissues of humans and other mammals.